The muscles of the lower limb are bundled into “compartments” surrounded by inelastic connective tissue called fascia. High-energy impact causes swelling and increased pressure within the muscle compartments that reduces blood flow and results in the condition called Acute Compartment Syndrome (ACS), see for example Pearse et al in “Acute Compartment Syndrome of the Leg” (British Medical J., Vol. 325, Iss. 7364, pp. 557-558) and Lee et al in “Acute Compartment Syndrome of the Leg with Avulsion of the Peroneus Longus Muscle: A Case Report” (J. Foot Ankle Surg., Vol. 48, Iss. 3, pp. 365-367), which is a well-recognized and common emergency. This intra-compartmental swelling is the result of increased size of the damaged tissues themselves following acute crush injury or from reperfusion of ischemic areas. It is usually not from a collection of free blood or fluid in the compartments. Presently, there is no reliable and reproducible test that confirms the diagnosis of ACS. A missed diagnosis or failure to cut the fascia to release pressure within a reasonable time, even just a few hours, can result in severe intractable pain, paralysis, and sensory deficits.
Currently, the diagnosis of ACS is made on the basis of physical exam and repeated needle sticks over a short time period to measure intra-compartmental pressures, see for example Falter in “Bedside Procedures in the ICU” (Springer, 2012) and Matsen et al in “Diagnosis and Management of Compartmental Syndromes” (J. Bone Joint Surg., Vol. 62, Iss. 2, pp. 286-291). Missed diagnosis of compartment syndrome continues to be one of most common causes of malpractice lawsuits in USA/Canada. Existing technology for continuous pressure measurements are insensitive, particularly in the deep tissues and compartments, and its use is restricted to highly trained personnel.
The usual cause of this condition is trauma although limb blood vessel surgery, limb blood clots, and hemorrhaging are other causes. However, crush injuries, burns, overly tight bandaging, prolonged compression of a limb during unconsciousness, anticoagulants, hemophilia, and tissue swelling under the skin can increase the risk of ACS. Typical symptoms may include: severe pain; feeling of tightness or fullness of muscles; swollen pale, shiny skin over affected area; and numbness or tingling. Symptoms may develop within 30 minutes to two hours, although in other cases, it may take days.
Undiagnosed compartment syndrome leads to muscle necrosis, contracture, and could eventually result in chronic infection or amputation. The only way to avoid these complications is early recognition and attendant decompression with a fasciotomy (large incision to release the fascial containment of the compartment). A method for the accurate and reproducible diagnosis of ACS, especially in the obtunded, polytrauma or distracted patient is yet to be developed. Resolution or clarification of the diagnosis of ACS would be a great asset for the patient population. Consequently, a large number of trauma surgeons face this diagnostic conundrum on almost a daily basis.
In today's clinical scenario, pressure measurements through the use of repeated needle sticks are the best means of determining the need for a fasciotomy. Although newer technologies, such as ultrasound, see for example Sellei et al in “Non Invasive Assessment of Acute Compartment Syndrome by Pressure Related Ultrasound: A Cadaver Study” (J. Bone Joint Surg., Brit. Vol. 94-B (Supp. XXXVII), pp. 521) and “Shadgan et al in “Diagnostic Techniques in Acute Compartment Syndrome of the Leg” (J. Orthopaedic Trauma, Vol. 22.8, pp. 581-587) and near infrared, see for example Arbabi et al in “Near-Infrared Spectroscopy: A Potential Method for Continuous, Transcutaneous Monitoring for Compartmental Syndrome in Critically Injured Patients” (J. Trauma and Acute Care Surg., Vol. 47, pp. 829), 1999, monitoring are being tested, but they all seem to have major problems with missing compartments and interfering with complete care of the patient.
Accordingly, there is a need for always-on minimally invasive devices that does not interfere with transportation or total care of the patient and allows continuous monitoring over an extended period given symptoms post-incident may take several days. It would be further beneficial to monitor all potential areas of interest without being labor-intensive, relying on highly educated technicians or being excessively user dependent, and offers low cost manufacturing to support widespread. It would be further beneficial for the technology employed to be compatible with integration of other sensor functions allowing in addition to accurately measuring pressure the measurement of oxygen partial pressure and temperature fluctuations in the limb compartments of patients at risk of developing ACS.
It would be further beneficial for temporary in-situ direct pressure monitors to be designed to be compatible with a battery-less Radio Frequency Identification Device (RFID)/Near Field Communication (NFC) platform, allowing the ACS sensors to be powered by wireless transfer of radio frequency electromagnetic energy. These small implantable silicon-based devices will revolutionize the management of trauma victims and minimize the devastating outcomes of compartment syndrome whilst being compatible with the ongoing drives to increased out-patient care and reduced hospitalization time. Whilst the small implantable silicon-based sensor microsystems according to embodiments of the invention are capable of measuring pressures under diverse conditions and being easily used by nurses in hospital settings they can also be easily deployed by paramedical personnel in cases of accidents, natural disasters, war, etc. In some instances the patient may become an outpatient and the monitoring continue until a subsequent outpatient appointment to remove the implanted sensor microsystems occurs. Beneficially, the implantable sensor microsystem will not interfere with movement of the patient during stabilization, surgery, intensive care stay, outpatient management, etc. and will ultimately, transform the management of trauma victims and minimize the devastating outcomes of compartment syndrome.
Other aspects and features of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.